Preparation of naphthalene and 2, 6-dimethylnaphthalene



United States Patent Ofifice 3,i53,h? Patented Get. 20, 1964 3,153,676PREPARATION OF NAPHTHALENE AND 2,6-DTHYLNAPHTHALENE Joseph G. Allen,Ridley Park, Pm, and Earl W. Mainsberg, Wilmington, Deh, assignors to unGil Qompany,

Philadelphia, Pa, a corporation of New Jersey Filed June 27, 1961, Ser.No. 119,84? 6 Claims. (Cl. 260668) This invention relates to thepreparation of condensed ring dicyclic aromatic hydrocarbons from chargestocks derived from gas oil and more specifically concerns an integratedprocess for producing naphthalene and 2,6- dimethylnaphthalene or,alternatively, a 2,6- and 2,7-dimethylnaphthalene concentrate.

Petroleum fractions which boil within the range of 400-550 F. generallycontain substantial amounts of alkylnaphthalenes, such as mono-, diandtrimethylnaphthalenes and in smaller quantity, the ethylnaphthalenes.Recycle fractions, which are formed in the cracking of petroleum stocksand which include this boiling range, often contain major proportions ofaromatic hydrocarbons that are mainly alkylnaphthalenes. Such fractionstypically may have aromatic contents varying within the range of 25-97%but usually contain between 50% and 95% aromatics depending upon theparticular operation in which the petroleum fractions are produced.These hydrocarbon charge stocks are obtained in both catalytic andthermal cracking processes and in operations in which combinations ofcatalytic and thermal cracking steps are utilized. Stocks having highalkylnaphthalene contents can also be obtained by extracting straightrun petroleum fractions of appropriate boiling ranges, such as kerosene,or catalytic fractions such as catalytic gas oil, with solvents, such asfurfural or sulfur dioxide, or by selective adsorption with silica gel.These aromatic concentrates may contain up to 100% aromatichydrocarbons.

The present invention is directed to the preparation of naphthalene and2,6-dimethylnaphthalene, or a concentrate of mixed 2,6- and2,7-dimethylnaphthalenes, from aromatic hydrocarbon charge stocks whichcomprise a mixture of alkylnaphthalenes and which can be derived fromsuch sources as referred to above. The charge stock typically includesthe two monomethylnaphthalenes, various dimethylnaphthalene isomersincluding 2,6-dirnethylnaphthalene and smaller amounts of theethylnaphthalenes.

There are ten possible dimethylnaphthalene isomers and most if not allof these occur in charge stocks of the kind described above. Due to theclose boiling points of these isomers, the separation from the mixtureof any particular isomer in high concentration is a difficult task. Aprocedure for obtaining 2,6-dirnethylnaphthalene from such charge stocksis particularly desirable, since this isomer is especially useful as anintermediate in the preparation of high quality resins. The presentinvention provides an integrated process for obtaining the 2,6-isomer inamount greater than the content of this isomer in the charge, whilesimultaneously converting other alkylnaphthalenes to naphthalene.

In one embodiment of the invention anaromatic concentrate of the 440-525F. boiling range, containing mainly monocyclic and dicyclic aromatichydrocarbons, is subjected to a preconditioningstep involvinghydrodesulfurization under conditions whereby sulfur is removed and themonocyclic aromatics largely are cracked to gasoline boiling rangeproducts. From the desulfurization product a fraction within the narrowboiling range of 500-510" F. is obtained by distillation under eflicient'fractionating conditions. We have found that this fraction containspractically all of the 2,6- and 2,7-dimethylnaphthalenes that werepresent in the charge, together with substantial amounts of 1,3-, 1,6-and 1,7-dimethylnaphthalenes and a small amount of ethylnaphthalenes.This fraction is processed in a manner, hereinafter fully described,whereby a 2,6-dimethylnaphthalene concentrate is produced and part ofthe other dimethylnaphthalenes are isomerized to form more of the2,6-isomer. Alkylnaphthalenes from the 500510 F. out which are not soisomerized are admixed with the portions of the desulfurization productboiling below 500 F. and above 510 F., and the mixture is subjected tohigh temperature hydrodealkylation to produce naphthalene. Thussubstantially all of the alkylnaphthalenes in the charge are convertedinto either naphthalene or 2,6-dimethylnaphthalene.

The invention is described more specifically with reference to theaccompanying drawing which is a schematic fiowsheet illustrating acombination process for producing naphthalene and2,6-dimethyh1aphthalene from a hydrocarbon stock containingalkylnaphthalenes.

The process as illustrated in the drawing involves a preliminaryextraction step followed by a catalytic hydrocracking-desulfurizationstep adapted to condition the alkylnaphthalene charge material for usein the other steps of the process. The charge, which enters the systemthrough line 10, is a gas oil fraction boiling in the range of 440-525F. and containing alkylnaphthalenes including monomethylnaphthalenes anddimethylnaphthalenes together with saturated hydrocarbons. It is fed toextractor 11 wherein it'is countercurrently extracted with anaromatic-selective solvent, which preferably is furfural, underconditions that will produce a highly aromatic extract. Raifinate, whichincludes the bulk of the saturated hydrocarbons and part of themonocyclic aromatics, is removed as indicated by line 12, and extract iswithdrawn via line 13. Conventional solvent separation means (not shown)are provided for recovering and recycling the solvent. The extractobtained from this step typically may contain about 60-65% dicyclicaromatics, 35% monocyclic aromatics and 0-5% saturates.

The heated extract, together with hydrogen from line 14, passes throughline 15 to a catalytic desulfurizerhydrocracker 16 which contains adesulfurization catalyst such as cobalt molybdate on alumina ormolybdenum disulfide on alumina. The conditions for conducting thiscatalytic conditioning step include a temperature within the range of800-980" F., a pressure of -1000 p.s.i.g., with a range of 200-500p.s.i.g. preferred, a hydrogen to hydrocarbon mole ratio of 3:1 to 25 :1and preferably 5:1 to 15:1, and a liquid hourly space velocity of 0.5 to10 (volumes of charge per hour per bulk volume of catalyst). Thehydrogen consumption under these conditions should be between 65-500s.c.f. per barrel of liquid feed per percent sulfur in the feed andpreferably between 200 and 400 set. per barrel. This conditioning stepeffects cracking of most of the'saturates and some of the monocyclicaromatics and also converts most of the sulfur in the hydrocarbon stockto hydrogen sulfide.

From hydrocracker 16 the reaction product is sent through line 17 tofractionator 18 from which normally gaseous components are removedoverhead through line H and a C -400 F. gasoline fraction is obtainedfrom line 20. The 400+ P. fraction which contains the alkylnaphthalenesis removed via line 21 and passes to a fractionation section(hereinafter described) for obtaining the narrow fraction from which the2,6-dimethylnaphthalene product is obtained.

Referring now to the high temperature dealkylation step for producingnaphthalene, a stream of mixed materials, obtained as hereinafterspecified and composed mainly of monomethyi and dim-ethylnaphthalenesand a small amount of ethylnaphthalenes, passes through line 22 togetherwith hydrogen introduced Via line 23 into dealkylator 24. In a preferredembodiment the dealkylation is eifected thermally without a catalyst.The conditions for this operation include a pressure of 150-1000p.s.i.g., preferably 200-500 p.s.i.g., a hydrogen to hydrocarbon moleratio within the range of 3:1 to 25:1 and preferably 5:1 to 1, aresidence time of 2-300 seconds with a preferred residence time of 10-60seconds, and a temperature above 1000" R, preferably within the range of12001400 F., suificient to effect dealkylation of alkylnaphthalenes. Inthis reaction only a partial dealkylation occurs. Hence the reactionproduct which leaves the reactor through line contains, in addition tothe desired naphthalene, unreacted naphthalenes and partiallydealkylated naphthalenes which can be recovered and recycled to thedealkylator.

Alternatively, the dealkylation reaction can be effected catalyticallyutilizing a desulfurizing catalyst such as cobalt molybdate ormolybdenum disuifide. The presence of the catalyst in this stepfacilitates the dealkylation reaction and in some cases permits it to becarried out at a lower temperature than that required for thermaldealkylation. The catalyst also effects the conversion of any remainingsulfur into hydrogen sulfide and hence permits the preparation ofnaphthalene having negliglibe sulfur content. The conditions for thecatalytic dealkylation step include a pressure of 150-1000 p.s.i.g. witha range of 200-500 p.s.i.g. preferred, a hydrogen to hydrocarbon moleratio of 5:1 to 25:1, a liquid hourly space velocity of 0.2-5.0, and atemperature above 1000 F, usually between 1100 F. and 1200 F.,sufiicient to dealkylate alkylnaphthalenes and convert any remainingsulfur mainly into hydrogen sulfide.

The reaction product from line 25 passes to fractionator 2.6 from whichgases and a C -400" F. aromatic gasoline cut are removed, respectively,from lines 27 and 28. The desired naphthalene product is taken from line29 as material boiling in the 400-450 F. range. Typically this fractionis composed predominantly of naphthalene and has a freezing point of78.6 C. and a sulfur content that is practically negligible.

The 450+ F. material withdrawn from fractionator 26 via line 30 iscomposed mainly of monornethyl and dimethylnaphthalenes. This streamalso contains a small amount of material boiling abovedimethylnaphthalenes which desirably should be removed. The stream ispassed through line 30 to fractionator 3?. from which analkylnaphthalene concentrate boiling in the range of 450-525 F. andsuitable for recycling is obtained overhead through line 32. The higherboiling material unsuitable for recycling is removed as bottoms via line33.

Referring now to the portion of the process for obtaining2,6-dimethylnaphthalene, the 400+ F. fraction of the desulfurizationproduct passes through line 21 to a distillation column 34 wherein asharp separation is made at a cut point of about 500 F. The 400-500 F.distillate passes through lines 35 and 22 as part of the charge todealkylation zone 24. The 500+ F. bottoms fraction is sent through lineto distillation column 37 wherein a sharp fractionation is made to splitout the narrow 500-510 P. out which is removed as distillate via line38. The 510+ F. material obtained as bottoms passes through lines 39, 40and 22 as additional charge to the dealkylator.

Each of the distillation columns 34 and 37 should be operated underefficient fractionating conditions employing, for example, 30-50theoretical plates and reflux ratios of the order of 30:1 to :1. We havefound that under these conditions the content of 2,6- plus2,7-dimethylnaphthalenes in the 500-510 P. fraction will be of the orderof 30-50%, with the remainder being the 1,3-, 1,6- and 1,7-isomers andethylnaphthalenes. Practically all of the 1,2-, 1,4-, 1,5-, 1,8- and2,3-dimethylnaphthalenes appear in the bottoms product withdrawn fromcolumn 37,

2,6-DMN isomer.

4 and these isomers are subsequently converted to naphthalene indealkylator 24.

The 500-510 F. cut from column 38 will contain a major proportion ofdimethylnaphthalenes (DMN) having the methyl groups on opposite rings ofthe naphthalene nucleus and minor proportions of ethylnaphthalene (EN)and DMN having methyl groups on the same ring of the naphthalenenucleus.

A typical composition of this material is as follows:

Percent Z-EN 1 8 l-EN 2 2,6-DMN 2 24 2,7-DMN 22 1,3 -DMN 13 1,7-DMN 171,6-DMN l4 1 Ethylnaphthalene. 2 Dimethylnaphthaleue.

This material is sent through lines 38 and 41 to a crystallizing andfiltering zone 3-2 wherein the material is chilled to a temperaturepreferably in the range of 0-30" C. and is filtered at such temperature.This tends preferentially to crystallize the 2,6- and 2,7-DMN and givesa filtrate from line 43 which typically contains -30% of the EN and60-75 of the 1,3-, 1, and 1,7-DMN that were present in the 500-510 F.cut. This procedure, by effecting removal of the bulk of the EN and1,3-DMN, prevents these components from building up in the cyclic systemhereinafter described. The filtrate passes from line 43 to lines 4-0 and22 through which it is introduced to the dealkylator 24.

The filter cake obtained as indicated by line 44 is then subjected to apartial melting in zone .5. This is done by warming the cake to atemperature preferably of about -85 F. while pressing it to squeeze outthe melted components which are filtered off through line 46. It hasbeen found that this procedure will give a residual filter cake,indicated by line 47, which has a 2,6-DMN content of the order of -95%and which contains about 25-35% of the 2,6-DMN that was present in thematerial fed to zone 45.

The filtrate from zone 45 passes through line 46 to an isomerizationzone 48 wherein it is subjected to conditions effective to cause a shiftin position of methyl groups and thus produce a further amount of thedesired A procedure for carrying out such isomerization reaction hasbeen described in Seitzer application United States Serial No. 28,753,filed May 12, 1960. It involves contacting the alkylnaphthalenes withany solid acidic cracking catalyst such as silica-alumina,silica-magnesia, silica-zirconia and acid activated clays. The reactiontemperature should be in the range of 300- 500 C. and more preferably325-400 C. The liquid space velocity can vary between 0.1 and 20 volumeshydrocarbon per volume catalyst per hour and more preferably ismaintained in the range of 0.5-6.0. It is desirable to conduct theisomerization at a low hydrocarbon partial pressure and generally in therange of 005-05 atmosphere, as otherwise coking tends to occur rapidlywith resultant deactivation of the catalyst. The low partial pressurecan be maintained either by holding a vacuum in isomerization zone 31 orby introducing an inert diluent along with the hydrocarbons, forexample, nitrogen, hydrogen, methane, propane, butanes, and the like.Whenever the activity of the catalyst has dropped enough to requireregeneration, this can be done in conventional manner merely by blowingair through the hot catalyst to burn off the coke deposits. Thereafterthe catalyst can be re-used for further isomerization.

Alternatively, the isomerization in zone 31 can be effected at lowtemperature using TIP-8P as catalyst. In practicing the isomerization inthis manner, the alkylnaphthalenes from line 4-6 are first dissolved ina suitable solvent, such as benzene or heptane, and the mixture iscontacted with the catalyst at a temperature preferably in the range of-30 C. and generally for several hours. Only a small amount of Bitneedbe used and the HF can be present in a large molar excess over the B1 toprovide sufiicient catalyst volume for good contact. After theisomerization the solvent can be removed by distillation (not shown).Generally, some amount of tarry material may be formed during this typeof isomerizing operation and it also can be removed by distillation.

By either of the above-described procedures for effecting isomerization,the dimethylnaphthalenes which have methyl groups on opposite rings ofthe naphthalene nucleus will be converted to an equilibrium mixture ofDMNs also having methyl groups on opposite rings, and those having bothmethyl groups on the same ring will be converted to an equilibriummixture or" DMNs likewise having methyl groups on the same ring. Inother words a shift of methyl groups from one ring to the other does notoccur. Thus the 1,3-isomer present in the 500-510 P. out does notconstitute a source for formation of the 2,6-DMN, and hence the1,3-isomer and any of the isomers to which it is converted in isomerizer48, such as the 1,4- and 2,3-isomers, eventually are converted tonaphthalene in dealkylator 24.

The isomerization product from zone 43 passes from line 49 to adistillation column 50 from which a distillate boiling up to 510 F. istaken overhead. This material, which contains essentially all of the2,6- and 2,7-DMN and part of the 1,3-, 1,6- and 1,7-isomers, is recycledthrough lines 51 and 41 to the crystallizer-filter 42. The higherboiling material obtained as bottoms through line 52 is essentially freeof the 2,6- and 2,7- DMN and contains the remainder of the 1,3-, 1,6-and 1,7-isomers along with any higher boiling isomers formed during theisomerization reaction. This material is sent through lines 52, 40 and23 to dealkylator 24 for conversion to naphthalene.

From the foregoing description it can be seen that essentially all ofthe alkylnaphthalenes present in the charge are utilized to produceeither naphthalene or 2,6- DMN as the two chemical products of theprocess. In addition the process produces gasoline which is highlyaromatic and hence has a high antiknock rating.

The above-described process can be modified, if desired, to obtain aconcentrate of mixed 2,6- and 2,7-DMN instead of the 2,6-DMNconcentrate. This can be done by first crystallizing the mixed feed tocrystallizer-filter 42 at a relatively low temperature, such as -lO C.to C. The filtrate from this step, which is enriched in EN and alsocontains part of the 1,3-, 1,6- and 1,7- DMN, is sent to thedealkylator. The filter cake is then warmed in zone 45 to a temperaturein the range of 65 C. while pressing and filtering. The resulting cakewill contain a major proportion of 2,6- and 2,7-DMN. For example, thecombined contents of these materials typically is 60-65% when the cakeis warmed at C. and 70-75% when it is warmed to 50 C. The resulting 2,6-and 2,7-concentrate can be separately processed, if desired, to obtaineach of the isomers in concentrated form. The filtrate from zone 45passes to isomerizer 48 to equilibrate the DMNs and produce additionalamounts of the 2,6- and 2,7-iso1ners for recycling by means of line 51.

We claim:

1. In a process involving hydrodesulfurizing a gas oil fraction boilingmainly in the range of 440-525 F. and containing mainly monocyclic anddicyclic aromatic hydrocarbons including monomethyl anddimethylnapthalene, separating from the desulfurization product materialcontaining alkylnaphthalene and subjecting such material to adealkylation reaction at a temperature above 1000 F. to producenaphthalene, the steps for recovering 2,6- dimethylnaphthalene as anadditional product which comprises: (l) separating from saiddesulfurization product a fraction boiling essentially in the range of500-5l0 F. and composed of a major proportion of dimethylnaphthalenehaving the methyl groups on opposite rings of the naphthalene nucleusand minor proportions of ethylnaphthalene and dimethylnaphthalene havingmethyl groups on the same ring of the naphthalene nucleus; (2) chillingsaid product to a temperature sufiiciently low to crystallize most ofthe 2,6- and 2,7-dimethylnaphthalene; (3) separating a filtrate enrichedin ethylnaphthalene from the crystallized material; (4) increasing thetemperature of the crystallized material to effect partial melting; (5)separating melted components from a cake constituting a2,6-dimethylnaphthalene concentrate; (6) isomerizing said meltedcomponents; (7) fractionating the isomerizate to obtain an overheadfraction boiling up to about 510 F. and composed mainly ofdimethylnaphthalene having methyl groups in opposite rings of thenaphthalene nucleus and a bottoms fraction boiling above 510 F; (8)recycling said overhead fraction to step (2); and (9) passing thefiltrate from step (3), the bottoms fraction from step (7) and materialsfrom step (1) boiling below 500' F. and above 510 F. to saiddealltylation reaction for conversion to naphthalene.

2. Process according to claim 1 wherein the temperature in step (2) isin the range of 0-30 C.

3. Process according to claim 2 wherein the temperature is increased to70-85 C. in step (4).

4. in a process involving hydrodesulfurizing a gas oil fraction boilingmainly in the range of 440-525 F. and containing mainly monocyclic anddicyclic aromatic hydrocarbons including monomethyl anddimethylnaphthalene, separating from the desulturization productmaterial containing alkylnaphthalene and subjecting such material to adealkyla ion reaction at a temperature above 1000 F. to producenaphthalene, the steps for recovering a concentrate of mixed 2,6- and2,7-dimethylnaphthalenes as an additional product which comprises: (1)separating from said desulfurization product a fraction boilingessentially in the range of 500-510 F. and composed of a majorproportion of dimethylnaphthalene having the methyl groups on oppositerings of the naphthalene nucleus and minor proportions ofethylnaphthalene and dimethylnaphthalene having methyl groups on thesame ring of the naphthalene nucleus; (2) chilling said product to atemperature sufiiciently low to crystallize most of the 2,6- and2,7-dimethylnaphthalene; (3) separating a filtrate enriched inethylnaphthalene from the crystallized material; (4) increasing thetemperature of the crystallized material to eilect partially melting;(5) separating melted components from a cake constituting a concentrateof mixed 2,6- and 2,7-dimethylnaphthalenes; (6) isomerizing said meltedcomponents; (7) fractionating the isomerizate to obtain an overheadfraction boiling up to about 510 F. and composed mainly ofdimethylnaphthalene having methyl groups in opposite rings of thenaphthalene nucleus and a bottoms fraction boiling above 510 F.; (8)recycling said overhead fraction to step (2); and (9) passing thefiltrate from step (3), the bottoms fraction from step (7) and materialsfrom step (1) boiling below 500 F. and above 510 F. to said dealkylationreaction for conversion to naphthalene.

5. Process according to claim 4 wherein the temperature in step (2) isin the range of 10 F. to +15 C.

6. Process according to claim 5 wherein the temperature is increased to20-65 C. in step (4).

References Cited in the file of this patent UNITED STATES PATENTS2,577,788 McAteer et al Dec. 11, 1951 2,741,646 Clark Apr. 10, 19562,910,514 Scott et al. Oct. 27, 1959 2,920,115 Friedman Jan. 5, 19603,001,932 Pietsch Sept. 26, 1961

1. IN A PROCESS INVOLVING HYDRODESULFURIZING A GAS OIL FRACTION BOILINGMAINLY IN THE RANGE OF 440-525* F. AND CONTAINING MAINLY MONOCYCLIC ANDCICYCLIC AROMATIC HYDROCARBONS INCLUDING MONOMETHYL ANDDIMETHYLNAPTHALENE, SEPARATING FROM THE DESULFURIZATON PRODUCT MATERIALCONTAINING ALKYLNAPHTHALENE AND SUBJECTING SUCH MATERIAL TO ADEALKYLATION REACTION AT A TEMPERATURE ABOVE 1000* F. TO PRODUCENAPHTHALENE, THE STEPS FOR RECOVERING 2,6DIMETHYLNAPHTHALENE AS ANADDITIONAL PRODUCT WHICH COMPRISES: (1) SEPARATING FROM SAIDDESULFURIZATION PRODUCT A FRACTION BOILING ESSENTIALLY IN THE RANGE OF500-510*F. AND COMPOSED OF A MAJOR PROPORTION OF DIMETHYLNAPHTHALENEHAVING THE METHYL GROUPS ON OPPOSITE RINGS OF THE NAPHTHALENE NUCLEUSAND MINOR PROPORTIONS OF ETHYLNBAPHTHALENE AND DIMETHYLNAPHTHALENEHAVING METHYL GROUPS ON THE SAME RING OF THE NAPHTHALENE NUCLEUS; (2)CHILLING SAID PRODUCT TO A TEMPERATURE SUFFICIENTLY LOW TO CRYSTALLIZEMOST OF THE 2,6- AND 2,7-DIMETHYLNAPHTHALENE; (3) SEPARATING A FILTRATEENRICHED IN ETHYLNAPHTHALENE FROM THE